The present invention relates generally to a mold and/or a molding machine for making ophthalmic devices. More particularly, this invention relates generally to a mold and/or a molding machine for making ophthalmic devices with many stock keeping units (SKUs).
U.S. Pat. No. 5,702,735 to Martin et al., the entire disclosure of which is hereby incorporated by reference, provides an apparatus for molding polystyrene lens curves, i.e., front curves or back curves, which are used for subsequent molding of soft contact lenses. The apparatus is designed to provide superior heat conduction capacity so as to minimize the molding cycle time, while simultaneously producing uniformly precise and accurate optical quality surfaces. Molten polystyrene is provided via a hot runner system to a plurality of mold cavities. In a mold used to make front curves, the convex surfaces of the mold provide the optical quality surfaces to the concave surfaces of the front curves produced thereby. The structural element which defines each convex surface includes a hollow cylindrical bushing and a removable power insert mounted therein, which may be changed so that the prescription strength of the contact lens to be formed by the lens curves may be varied. In a first embodiment, the power insert includes only a convex surface at its operational end. In a second embodiment, the power insert includes an annular flat surface surrounding the convex surface, defining at the junction therebetween a discontinuity of curvature, which imparts a sharp edge to the front curve formed thereby. Cooling water is pumped into the core of the inserts to cool the inserts during the molding process, which complicates the process of changing the inserts. The power insert may be constructed of various materials including pure steel, brass, copper chromium, or cobalt-nickel alloyed martensitic steel. The power insert may be coated with a surface layer of nickel phosphor or silicone oxide, or chrome nitride. These layers may be turned to their proper thicknesses and dimensions by diamond cutters, and they may be thermally hardened.
U.S. Pat. No. 4,565,348 to Larsen, which is also incorporated by reference, discloses another prior art approach to manufacturing lens curves. Pursuant to this prior art approach, the lens curves are molded as a set of eight lens curves carried on a frame in a 2xc3x974 array. FIG. 3 of the Larsen patent illustrates a molded frame carrying a 2xc3x974 array of concave front curves, while FIG. 5 therein shows a molded frame carrying a 2xc3x974 array of back curves. The cluster assembly of the frame and lens curves is manufactured by injection molding the assembly as one piece with the lens curves being secured within an outer rectangular frame by small struts extending between the frame and the lens curves. The height of the frame is such that the surfaces of the lens curves are protected from scratching and mechanical damage during handling, and the frame in general has a shape facilitating stacking and handling. This prior art approach of molding such polystyrene lens curves in a cluster assembly typically takes approximately twenty-four (24) seconds, which is too long for the efficient production of such polystyrene lens curves.
In this prior art approach, complementary sets of front and back curves are used in the production of hydrogel contact lenses by molding a reaction mixture wherein the mixture is preferably dissolved in a non-aqueous, water-displaceable solvent. After a dosing step in which the front curves are substantially filled with the reaction mixture, the concave front curves are covered with the back curves in a manner in which no air bubbles are trapped beneath the back curves. Back curves are placed on the polymerizable mixture in the front curves as individual units; therefore, prior to this step, the back curves are separated from their frames by breaking or cutting. The back curves are preferably held by a mechanical device while they are separated from the frame which thereafter places the back curves on the front curves. The reaction mixture is then subjected to conditions whereby it polymerizes, e.g. irradiation with actinic visible or ultraviolet radiation, to thereby produce a polymer in the shape of the desired hydrogel lens. After the polymerization process is completed, the two lens curves are separated (called demolding); typically leaving the contact lens in the front curve, from which it is subsequently displaced. Typically the front and back curves are used once to mold a single contact lens. After the polymerization is complete, the diluent is displaced with water to produce a hydrated lens.
U.S. Pat. No. 5,782,460, and WO 98/42497 disclose a method of making hydrogel contact lenses by molding a material which has been polymerized but is at least partially uncrosslinked within reusable molds. Crosslinking of the polymer is by UV radiation; therefore, the mold consists of a UV-permeable material, such as quartz, or polymeric materials. One or more contact lenses can be molded in each mold tool.
U.S. Pat. No. 5,451,155 to Kok et al., the entire disclosure of which is hereby incorporated by reference, discloses an arrangement for manufacturing goods, such as compact discs, by injection molding, providing a vertical injection molding machine including two holders that support mold plates. The mold plates are adjustable with respect to each other between a first position, in which the molding plates define a cavity, into which material is injected by the injection molding machine during operation, so that the particular molded good is formed, and a second position, in which the molding plates have been moved some distance apart, while the formed good is being removed. On each side of the injection molding machine, transport devices are provided which move the holder and molding plates from a position located at some distance from the injection molding machine to a position suitable for cooperation with the injection molding machine. The transport devices and the holders are detachably coupled. It is also disclosed that a holder may be provided with a new molding plate at some distance from the machine while the machine is in operation. For exchanging the molding plates and holders, it is only necessary to discharge the holder supporting the molding plate used so far, and to move the new holder and molding plate into position. This type of exchange of molding plates provides for a quick and simple retooling while minimizing the downtime of the injection molding operation.
There is a need in the art to improve the molds and molding technology for making ophthalmic devices, particularly for ophthalmic devices with many stock keeping units (SKUs). The term xe2x80x9cstock keeping unitsxe2x80x9d refers to different devices, e.g. different products. For example, contact lenses having different powers, and/or cylinders and/or axis values each combination of which would represent a different SKU, each SKU being manufactured using different molds or a different orientation of the molds or different reactive mixtures within the molds.
This invention provides a mold and a molding system comprising a mold comprising a first mold half which works in conjunction with a second mold half for forming ophthalmic devices wherein said first mold half comprises at least one changeable cassette comprising inserts for forming said ophthalmic devices. This mold can be used to make ophthalmic devices; however, this mold is preferably used in an automated molding machine, more preferably in an injection molding machine. This invention is preferably used to make lens curves which are in turn used to make contact lenses.
This invention further provides a vertical injection molding machine comprising a mold, preferably having at least one cassette, in which the machine can quickly change one mold half for another, and the machine is capable of making ophthalmic devices.
This invention further provides a mold in which two different optical quality ophthalmic devices are made in a single mold.
The molds and molding system comprising a mold of this invention make it possible to quickly change the optical characteristics of the ophthalmic devices, which are produced using the molds of this invention. The molds comprising one or more cassettes make it possible to quickly change the cassette(s) thereby making it possible to efficiently make ophthalmic devices with many stock keeping units (SKUs) using one or a small number of mold halves comprising changeable cassettes. These molds are particularly suited for directly or indirectly producing contact lenses having many spherical powers, aspherical powers or multifocal powers.
Accordingly, it is a primary object of the present invention to provide an improved mold and moldingsystem comprising a mold comprising a first mold half and a second mold half wherein said first mold half comprises at least one changeable cassette comprising multiple inserts for forming ophthalmic devices. The first mold half and the second mold half are adjustable with respect to each other between a first position, in which the mold halves form a mold cavity into which a material can or has been introduced so as to form molded ophthalmic devices, and a second position, in which the mold halves have been moved some distance apart preferably while means are provided for removing the molded ophthalmic devices and a second position, in which the mold halves have been moved some distance apart preferably while means are provided for removing the molded ophthalmic devices.
One embodiment of the invention provides a mold half comprising one or more changeable cassettes having inserts that are cooled indirectly; thereby making it easier to remove and interchange the cassette(s).
Another embodiment of the invention improves the removal of the molded ophthalmic devices from the mold by providing an air ejection system. In contrast to prior art which used ejector pins, air ejection does not distort the ophthalmic device and for the preferred embodiment can be done while the molded ophthalmic devices are at a higher temperature.
Another embodiment of the invention provides a mold and molding system comprising a mold designed such that either one or more of the cassette(s) and/or the mold half or halves comprising the cassette(s) can be changed to provide for a different ophthalmic device or devices, that is, different SKUs. In the preferred application, the ophthalmic devices formed using the mold are front curves and back curves used to make contact lenses. The front curves and back curves are preferably molded in a xe2x80x9cfamily moldxe2x80x9d arrangement, which means that both mold halves of the mold include complementary inserts for forming both front curves and back curves (convex protrusions and and concave indentations). One mold half preferably comprises a cassette having inserts for front curves, and another cassette having inserts for back curves. In this embodiment, only one mold half needs to be changed to change the front curves and back curves, or one cassette on the mold half can be changed to change either the front curves, or back curves provided by the mold. Changing one mold half or changing the cassette will change the front curves and/or back curves and will result in the production of lenses of different SKUs produced using the front curves and back curves. This arrangement is possible, because only one surface of the front and back curves has an optically critical side whereas the other side is not optically critical. Thus, if the optically critical sides of the lens curves are formed by the changeable cassette side of the mold, the optical characteristics of the lens curves can be changed without changing both sides of the mold.
Another object is to provide an improved mold for making front curves and back curves having the same wall thicknesses for the front curve and back curve.